Rift

Rift is set in a fantasy world called Telara, which is the focal point of several different elemental Planes. These Planes are realities representing the elemental forces of Air, Fire, Water, Earth, Life, and Death, and it is at the one point where every one of these Planes intersect with each other that Telara exists. Each Plane is governed by a Dragon-deity, which is the personification of that elemental force. Through the actions of the Dragon of Extinction, Regulos, the various Dragons have united in an alliance known as the Blood Storm, for the purpose of invading Telara and gaining use of the intersection of all of their realms. In the past, the Blood Storm was defeated by the inhabitants of Telara with the help of the Vigil, the most powerful of the native gods of Telara.

Regulos was cast out into the elemental Planes, while its five compatriots were trapped within Telara and chained beneath a Ward designed to close Telara off from external threats. However, recently, Regulos has gained entry to Telara, destroying the Ward and causing Rifts to open to the elemental Planes, feeding the strength of the trapped Dragons and allowing their minds to enter in a bid to destroy Telara’s defenders. Opposing Regulos within Telara are two factions: the Guardians and the Defiant. The conflict between these two factions serves as another source of tension and gameplay. Players have the role of Ascended, superhuman resurrected warriors whose task is to defeat the forces of Regulos and cleanse Telara forever of the threat of the Storm.

Rifts are areas of elemental instability that represent the intrusion of elemental planes into the land of Telara. Once opened, these rifts begin to spawn monsters that proceed to march towards important points on the map. It is then up to players to defeat these monsters and to close the rift. If rifts are left unchecked, the invading monsters will eventually conquer large portions of the map, killing and significantly impairing the players in that area.

Taken from Wikipedia.